Because the interpretation of data from the type of experiments to be described requires the demonstration of considerable specificity in the protocol of labeling, antigen receptors on cells shall be studied first because here the outcome is at least partially predictable. A similar approach will then be used to analyze antigen receptors on T cells where the results are less predictable. l. To compare the ability of several affinity labeling reagents to compete with unmodified antigen in binding to lymphocyte surface receptors using an assay capable of allowing the calculation of the association constant of the inhibitor. 2. To study any changes in antigen binding capabilities which occur after selection of a specific lymphocyte population by affinity chromotography. 3. To determine the specificity and localization of affinity labeling reagents used on intact lymphocytes. 4. To purify small amounts of antigen receptors. 5. To analyze the structure of the antigen receptor by biochemical and serological methods.